Could Trump cull US out of Nato and what would appear if he did? | Luke Harding

Donald Trump has come close to suggesting that the United States might unilaterally exit from Nato if other member states failed to dramatically increase their spending on the military bloc.

According to diplomats, he plunged the summit into chaos on Thursday by saying that the US would “go it alone”, if European states failed to boost their spending to at least 2% by January.

At an emergency press conference, Trump later appeared to row back from this threat, claiming that Nato members had agreed to commit an extra $33bn (£25bn). He said it was “a little tough for a little while” and that he had told the Europeans he would be “very unhappy” if they did not up their spending “substantially”.

But, he added, a “tremendous amount of progress” had been made. Nato was now “much stronger”, he added, with spending “rocketing” upwards.

Could Trump withdraw from Nato?

In his comments, Trump appeared to suggest that he had the power to withdraw from Nato without the approval of the US Congress.

In fact, the organisation – established in 1949 and approved by the US Senate in 1953 – is established by a formal and binding treaty.

This means that Trump is not able to use his executive power to pull America out of the alliance, in contrast to other international agreements such as the Iran nuclear deal or the Paris climate agreement, both of which Trump has withdrawn from.

Trump would normally first need to win approval in the Senate and to persuade Republican senators that the move was necessary and in the US’s long-term security interests.

Unsurprisingly, Trump’s apparent threat caused dismay on Thursday among European allies. There is no certainty it would attract support in Washington from leading Republicans.

What would the consequences be?

Leaving Nato would be a seismic step, previously unthinkable, that would shake up a western alliance that has endured for more than 70 years. It would also be a boon to Russia and its leader, Vladimir Putin, whom Trump will meet on Monday in Helsinki.

Ultimately, a decision by the White House to abandon Nato could be challenged legally and end up in the US Supreme Court. Trump now has a majority in the court and is likely to succeed in winning approval for his conservative nominee, Brett Kavanaugh.

For now, it appears that Trump’s threat is just that. In more emollient tones, Trump claimed on Thursday that the US’s commitment to Nato was “very strong and “remains very strong” following negotiations.

Jens Stoltenberg, the Nato secretary general, is now left with a headache: what to do if Trump returns to this theme of departure and how the alliance might survive were America really to leave?